Extrinsic back muscles are one of two main sets of spinal extensor muscles. (The other set is intrinsic.) Extrinsic and intrinsic back muscles are grouped according to their location, and their function.
Both extrinsic and intrinsic back muscles are necessary for spinal support because most of our weight is in front of us. Without powerful muscles located in the back, we would likely experience collapsed posture and limited trunk movement most of the time.
The extrinsic back muscles are located towards the outside of the body. They, too, are divided into two groups — the superficial extrinsic back muscles and the intermediate extrinsic back muscles.
This article explains the superficial layer of the extrinsic back muscles.
While overall, the extrinsic back muscles help control arm movement and play a role in breathing, the hallmark of the superficial layer is the arm movements. (Breathing is greatly influenced by the intermediate extrinsic layer.)
Muscles of the Superficial Extrinsic Group
The superficial extrinsic back muscle group is comprised of 4 muscles: The trapezius, latissimus dorsi, levator scapula, and the rhomboids.
One of the most notable features of the trapezius muscle is its shape. The trapezius (called “traps” for short) is a large triangular-shaped muscle located at the mid and upper back, and at the neck and shoulders.
This muscle has a number of functions, not the least of which involves moving the shoulder blades (these are the flat — also triangularly shaped — bones that sit on the back of the ribcage.) Other functions of the trapezius include contributing to head and neck motions and assisting with breathing.
The trapezius muscle has 3 parts: The upper, middle and lower. Learn more specific information about the attachment sites and the functions of the trapezius muscle.
Another triangularly shaped muscle, the latissimus dorsi, is a key player when you use your arms to pull your body weight. For this reason, it is often referred to as the “swimmer's muscle.” (The latissimus dorsi is also called the “lats” for short.) The lats assist with breathing, too.
The lats take up a good amount of space in the low and mid-back. They start at the bottom of the thoracic spine and ribs, the thoracolumbar fascia and part of your hip bone. They then taper into a fine point that inserts on the inside of the upper arm bone.
The levator scapula muscle starts at the neck and travels down to attach on the media corner of the top of the shoulder blade. Its job is to lift the shoulder blade up toward the ears. This action is unfortunately constantly “on” for most of us, which can result in lots of neck and shoulder tension.
The rhomboid muscles are two parallelogram-shaped muscles (right and left) that extend from the midline of the spine to the inner border of the scapula (shoulder blade bone).
Each rhomboid consists of a major and minor part, called, respectively the rhomboid major and the rhomboid minor. Though two separate structures, the major and minor make one overall shape and act as a unit to squeeze the shoulder blades together.
Because of its action (of squeezing the shoulder blades together), targeting the rhomboids for posture improvement exercise may be a good idea. The action of squeezing the shoulder blades together (towards the spine) may help reverse the effects of sitting at the computer and/or other forms of postural kyphosis. In fact, there is an upper body posture exercise you might want to try right now.